[LTP] [PATCH V3] ltp: Add a zero latency constraint for the timer tests library

[Jan Stancek]

----- Original Message -----
> 
> On Intel, the firmware usually overrides the kernel power management
> decision by auto-promoting the idle states.
> 
> So it is possible it is the case for you. With a process keeping the CPU
> "busy" that prevents the firmware to go to a deepest idle state.
> 
> I see it is a Xeon platform. You can try by checking the
> performance/power balance option in the BIOS. AFAIR, there is
> performance aggressive, power aggressive, balanced-performance+ and
> balanced-power+ and balanced.
> 
> Can you check this option ?

I played a lot of with BIOS settigns, but none of:
 speedstep, c-states, turboboost, S3 disable
made any difference.

As it turned out, this is a kernel bug which was fixed in 4.15 by:
  commit b511203093489eb1829cb4de86e8214752205ac6
  Author: Len Brown <len.brown@intel.com>
  Date:   Fri Dec 22 00:27:55 2017 -0500
    x86/tsc: Fix erroneous TSC rate on Skylake Xeon

Numbers look great with this patch:

tst_timer_test.c:356: INFO: CLOCK_MONOTONIC resolution 1ns
tst_timer_test.c:368: INFO: prctl(PR_GET_TIMERSLACK) = 50us
tst_timer_test.c:275: INFO: poll() sleeping for 1000us 500 iterations, threshold 450.01us
tst_timer_test.c:318: INFO: min 1052us, max 1056us, median 1052us, trunc mean 1052.00us (discarded 25)
tst_timer_test.c:333: PASS: Measured times are within thresholds
tst_timer_test.c:275: INFO: poll() sleeping for 2000us 500 iterations, threshold 450.01us
tst_timer_test.c:318: INFO: min 2019us, max 2055us, median 2052us, trunc mean 2051.95us (discarded 25)
tst_timer_test.c:333: PASS: Measured times are within thresholds
tst_timer_test.c:275: INFO: poll() sleeping for 5000us 300 iterations, threshold 450.04us
tst_timer_test.c:318: INFO: min 5052us, max 5053us, median 5052us, trunc mean 5052.15us (discarded 15)
tst_timer_test.c:333: PASS: Measured times are within thresholds
tst_timer_test.c:275: INFO: poll() sleeping for 10000us 100 iterations, threshold 450.33us
tst_timer_test.c:318: INFO: min 10052us, max 10053us, median 10052us, trunc mean 10052.26us (discarded 5)
tst_timer_test.c:333: PASS: Measured times are within thresholds
tst_timer_test.c:275: INFO: poll() sleeping for 25000us 50 iterations, threshold 451.29us
tst_timer_test.c:318: INFO: min 25052us, max 25053us, median 25052us, trunc mean 25052.46us (discarded 2)
tst_timer_test.c:333: PASS: Measured times are within thresholds
tst_timer_test.c:275: INFO: poll() sleeping for 100000us 10 iterations, threshold 537.00us
tst_timer_test.c:318: INFO: min 100103us, max 100103us, median 100103us, trunc mean 100103.00us (discarded 1)
tst_timer_test.c:333: PASS: Measured times are within thresholds
tst_timer_test.c:275: INFO: poll() sleeping for 1000000us 2 iterations, threshold 4400.00us
tst_timer_test.c:318: INFO: min 1001003us, max 1001004us, median 1001003us, trunc mean 1001003.00us (discarded 1)
tst_timer_test.c:333: PASS: Measured times are within thresholds

Regards,
Jan

> 
> On 12/12/2017 16:04, Jan Stancek wrote:
> > 
> > 
> > ----- Original Message -----
> >> On 12/12/2017 15:48, Jan Stancek wrote:
> >>> Hi,
> >>>
> >>> I'm running into similar problem on "Dell Precision 5820 tower", with
> >>> Intel(R) Xeon(R) W-2133 CPU @ 3.60GHz, but I can't find any /proc /sys
> >>> knob that would help.
> >>>
> >>> # uname -r
> >>> 4.14.5
> >>>
> >>> # cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_governor
> >>> performance
> >>> performance
> >>> performance
> >>> performance
> >>> performance
> >>> performance
> >>> performance
> >>> performance
> >>> performance
> >>> performance
> >>> performance
> >>> performance
> >>>
> >>> Any timer related tests are reliably failing on longer timeouts:
> >>> ---
> >>> tst_test.c:934: INFO: Timeout per run is 0h 05m 00s
> >>> tst_timer_test.c:356: INFO: CLOCK_MONOTONIC resolution 1ns
> >>> tst_timer_test.c:368: INFO: prctl(PR_GET_TIMERSLACK) = 50us
> >>> tst_timer_test.c:275: INFO: poll() sleeping for 1000us 500 iterations,
> >>> threshold 450.01us
> >>> tst_timer_test.c:318: INFO: min 1095us, max 1098us, median 1096us, trunc
> >>> mean 1095.99us (discarded 25)
> >>> tst_timer_test.c:333: PASS: Measured times are within thresholds
> >>> tst_timer_test.c:275: INFO: poll() sleeping for 2000us 500 iterations,
> >>> threshold 450.01us
> >>> tst_timer_test.c:318: INFO: min 2062us, max 2138us, median 2137us, trunc
> >>> mean 2135.98us (discarded 25)
> >>> tst_timer_test.c:333: PASS: Measured times are within thresholds
> >>> tst_timer_test.c:275: INFO: poll() sleeping for 5000us 300 iterations,
> >>> threshold 450.04us
> >>> tst_timer_test.c:318: INFO: min 5262us, max 5263us, median 5262us, trunc
> >>> mean 5262.20us (discarded 15)
> >>> tst_timer_test.c:333: PASS: Measured times are within thresholds
> >>> tst_timer_test.c:275: INFO: poll() sleeping for 10000us 100 iterations,
> >>> threshold 450.33us
> >>> tst_timer_test.c:318: INFO: min 10318us, max 10471us, median 10471us,
> >>> trunc
> >>> mean 10469.07us (discarded 5)
> >>> tst_timer_test.c:321: FAIL: poll() slept for too long
> >>
> >> Are you running the tests with this zero latency patch included ?
> > 
> > Yes, I'm running ltp release 20170929, which has your patch.
> > 
> > ...
> > [pid 18276] 09:59:21.379883 open("/dev/cpu_dma_latency", O_WRONLY) = 3
> > [pid 18276] 09:59:21.379906 write(3, "\0\0\0\0", 4) = 4
> > ...
> > 
> > I tried it without that patch, and it started failing more with smaller
> > timeouts.
> > 
> > Regards,
> > Jan
> > 
> >>
> >>
> >>> SCHED_OTHER or SCHED_FIFO -> FAIL
> >>> intel_idle.max_cstate=0 processor.max_cstate=1 -> FAIL
> >>> echo 1 > /sys/devices/system/cpu/intel_pstate/no_turbo -> FAIL
> >>> idle=halt -> FAIL
> >>> idle=poll -> FAIL
> >>>
> >>> Only thing I found to help is to keep CPU slightly busy with
> >>>   taskset -c 1 sh -c "while [ True ]; do usleep 100; done"
> >>>
> >>> After that it started to PASS:
> >>>
> >>> # taskset -c 1 ./poll02
> >>> tst_test.c:934: INFO: Timeout per run is 0h 05m 00s
> >>> tst_timer_test.c:356: INFO: CLOCK_MONOTONIC resolution 1ns
> >>> tst_timer_test.c:368: INFO: prctl(PR_GET_TIMERSLACK) = 50us
> >>> tst_timer_test.c:275: INFO: poll() sleeping for 1000us 500 iterations,
> >>> threshold 450.01us
> >>> tst_timer_test.c:318: INFO: min 1004us, max 1325us, median 1072us, trunc
> >>> mean 1149.29us (discarded 25)
> >>> tst_timer_test.c:333: PASS: Measured times are within thresholds
> >>> tst_timer_test.c:275: INFO: poll() sleeping for 2000us 500 iterations,
> >>> threshold 450.01us
> >>> tst_timer_test.c:318: INFO: min 2007us, max 2326us, median 2075us, trunc
> >>> mean 2158.64us (discarded 25)
> >>> tst_timer_test.c:333: PASS: Measured times are within thresholds
> >>> tst_timer_test.c:275: INFO: poll() sleeping for 5000us 300 iterations,
> >>> threshold 450.04us
> >>> tst_timer_test.c:318: INFO: min 5006us, max 5345us, median 5074us, trunc
> >>> mean 5146.84us (discarded 15)
> >>> tst_timer_test.c:333: PASS: Measured times are within thresholds
> >>> tst_timer_test.c:275: INFO: poll() sleeping for 10000us 100 iterations,
> >>> threshold 450.33us
> >>> tst_timer_test.c:318: INFO: min 10004us, max 10364us, median 10075us,
> >>> trunc
> >>> mean 10128.61us (discarded 5)
> >>> tst_timer_test.c:333: PASS: Measured times are within thresholds
> >>> tst_timer_test.c:275: INFO: poll() sleeping for 25000us 50 iterations,
> >>> threshold 451.29us
> >>> tst_timer_test.c:318: INFO: min 25006us, max 25359us, median 25072us,
> >>> trunc
> >>> mean 25137.48us (discarded 2)
> >>> tst_timer_test.c:333: PASS: Measured times are within thresholds
> >>> tst_timer_test.c:275: INFO: poll() sleeping for 100000us 10 iterations,
> >>> threshold 537.00us
> >>> tst_timer_test.c:318: INFO: min 100010us, max 100372us, median 100125us,
> >>> trunc mean 100167.78us (discarded 1)
> >>> tst_timer_test.c:333: PASS: Measured times are within thresholds
> >>> tst_timer_test.c:275: INFO: poll() sleeping for 1000000us 2 iterations,
> >>> threshold 4400.00us
> >>> tst_timer_test.c:318: INFO: min 1000843us, max 1000920us, median
> >>> 1000843us,
> >>> trunc mean 1000843.00us (discarded 1)
> >>> tst_timer_test.c:333: PASS: Measured times are within thresholds
> >>>
> >>> Summary:
> >>> passed   7
> >>> failed   0
> >>> skipped  0
> >>> warnings 0
> >>>
> >>> Any ideas?
> >>>
> >>> Regards,
> >>> Jan
> >>>